TN-C (calcium binding component of troponin) evolved by gene tetraplication from the same basic unit (E helix, EF calcium binding loop and F helix) as did the gene triplicated protein, MCBP (carp muscle calcium calcium binding parvalbumin). We are now completing the difference Fourier refinement and subsequent analysis of the crystal structure of MCBP. We are beginning a detailed model building prediction of the TN-C structure based on its homology with MCBP. We will test several predictions of this TN-C model concerning its lanthanide binding and tyrosine flourescence. We will purify TN-C and the entire troponin complex (TN-C, TN-T AND TN-I) from several species with the goal of crystallizing them for subsequent crystal structure determination.